1. Field of the Invention
The present invention relates to an exposure method, an exposure apparatus, and a method of manufacturing a device.
2. Description of the Related Art
Wafer processing principally includes alignment processing such as prealignment and global alignment for aligning a wafer, and exposure processing. To improve the wafer productivity, that is, the throughput, various efforts are made to shorten the time taken for each processing.
In alignment processing, a plurality of marks is selected from alignment marks formed on the wafer as sample shots, and the positions of these marks are measured. The sample shots used are as shown in FIG. 4. A low-magnification alignment mark WML and high-magnification alignment mark WMH are formed in each shot. In prealignment, the position of the low-magnification alignment mark in a first sample shot SL1 is measured using a low-magnification scope first, and that of the low-magnification alignment mark in a sample shot SL2 is measured next. Wafer prealignment is performed based on the measured positions of the two low-magnification alignment marks SL1 and SL2.
After the wafer prealignment is performed, global alignment, that is, main alignment of the wafer is performed. In global alignment, several shots on the wafer are measured by taking account of a tradeoff between the productivity of ICs or LSIs and the alignment accuracy. For example, to attain a sample shot arrangement optimum for global alignment, sample shots are arranged outside as much as possible, except the wafer periphery, so as to be nearly symmetrical about the wafer center and nearly uniformly distributed on the circumference. In global alignment, the positions of high-magnification alignment marks are measured in the order of sample shots SH3, SH4, SH5, and SH6 using a high-magnification scope, thereby performing main alignment of the wafer.
After the main alignment is performed, the wafer stage is driven to a first exposure shot E1, and it is exposed. Subsequently, each shot is exposed while driving the wafer stage.
Japanese Patent Laid-Open Nos. 2005-217333 and disclose details of this conventional method.
The above-mentioned conventional method is effective for a semiconductor exposure apparatus which exposes a wafer by quickly, precisely aligning it. However, the conventional method requires a long alignment time because, for prealignment, it measures the positions of two low-magnification alignment marks on each wafer to be exposed.